Mist generating apparatus are known and are used in a number of fields. For example, such apparatus are used in both fire suppression and cooling applications, where the liquid droplet mists generated are more effective than a conventional fluid stream. Examples of such mist generating apparatus can be found in WO2005/082545 and WO2005/082546 to the same applicant.
A problem with other conventional mist generating apparatus is that not all of the working fluid being used is atomized as it passes through the apparatus. Although the majority of the working fluid is atomized upon entry into the mixing chamber of the apparatus, some fluid is pulled into the chamber but is not atomized. The non-atomized fluid can stick to the wall of the mixing chamber and flow downstream along the wall to the outlet nozzle, where it can fall into the atomized fluid stream. This can cause the creation of droplets which are of non-uniform size. These droplets can then coalesce with other droplets to create still larger droplets, thus increasing the problem and creating a mist of non-uniform droplets.
In cooling applications in particular, the uniformity of the size of the droplets in the mist is important. In turbine cooling applications, for example, droplets which are over 10 μm in diameter can cause significant damage to the turbine blades. It is therefore important to ensure control and uniformity of droplet size. Optimally sized droplets will evaporate, thus absorbing heat energy and increasing the air density in the turbine. This ensures that the efficiency of the turbine is improved. Existing turbine cooling systems employ large droplet eliminators to remove large droplets and thus prevent damage to the turbine. However, such eliminators add to the complexity and manufacturing cost of the apparatus.
It is an aim of the present invention to obviate or mitigate one or more of the aforementioned disadvantages.